The task of this paper is to explain how pension system in Croatia works and on the concrete example, do research about it, involving methods for the calculation of average. Data used for this research, are taken from Croatian Pension Insurance Institute. Pensions in Croatia are classified into three main groups: Old-age, Invalidity and Survivor's. There are different principles for achieve rights for each group. The methods which will be used in this research are: arithmetic mean, median and mod. Formulas that will be used in this paper are based on grouped data. Their assignment is to define average pension, usually paid pensions and define how many pension beneficiaries has less than average pension is, and how many of them has more then average.